CTFL-v4 Fundamentals of Testing Practice Question
Which of the following describes the 'pesticide paradox' in software testing?
⚠ Common exam trap
Test-takers frequently confuse the pesticide paradox with defect clustering, wrongly assuming that finding many bugs in one module means the same thing as tests losing their effectiveness over time.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Repeating the same test cases will eventually stop finding new defects.
The pesticide paradox explains that repeatedly running the same tests will eventually lead to those tests failing to find new bugs, as the software becomes 'immune' to them. This is why testers must regularly review and update their test suites. By introducing new test cases and techniques, testers ensure that the test suite remains effective at identifying defects that were previously missed by existing, static test coverage strategies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Testers find fewer bugs as they spend more time on a module.
Why it's wrong here
This describes the natural decrease in defect density as a system matures, but it does not specifically describe the pesticide paradox. The paradox is about the test suite's diminishing ability to find new bugs, not necessarily the amount of time spent or the inherent quality of the module itself.
- ✓
Repeating the same test cases will eventually stop finding new defects.
Why this is correct
The pesticide paradox states that if the same tests are executed repeatedly, they will stop finding new defects. To find more bugs, existing tests need to be updated, and new, different tests need to be added to the suite to maintain test effectiveness throughout the software development lifecycle.
- ✗
Automated tests are less effective than manual tests.
Why it's wrong here
This is a misconception. Both manual and automated tests have their own strengths and weaknesses. The pesticide paradox applies to any test suite, regardless of whether it is manual or automated, if the test cases remain static and are not updated to cover new functionality or different execution paths.
- ✗
Testing becomes more expensive over time.
Why it's wrong here
While testing costs can fluctuate, the pesticide paradox specifically refers to the effectiveness of test cases, not the cost. While updating tests does incur a cost, it is a necessary investment to ensure that the testing remains relevant and capable of uncovering new defects within the evolving software system.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISTQB exam blueprint
This CTFL-v4 practice question is part of Courseiva's free ISTQB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CTFL-v4 exam.